Active electro-optic missile warning system

ABSTRACT

A threat detection system and method protects an object of interest (such as, but not limited to, manned and unmanned aircrafts, vehicles, vessels, and buildings) from potential weapons (such as, but not limited to, a missile, an aircraft, a vehicle, a vessel, or the like). The threat detection system transmits a hi-powered, extremely short-pulsed non-directional laser signal. Because the pulse time of the laser signal is so short (a few tenths of a nanosecond), the laser signal is substantially only reflected off optics that are pointed or aimed at the object to be protected. The reflected laser signals are received by the threat detection system and are then compared with the transmitted laser signals to determined the direction, speed, distance and potentially identity of the potential weapon. Because the threat detection system is not based on movement alone, it is capable of detecting a potential weapon while in flight or prior to launch.

RELATED APPLICATION

This application is related to and claims priority from U.S. provisionalApplication No. 60/682,140 filed May 18, 2005 entitled ActiveElectro-Optic Missile Warning System which is incorporated fully hereinby reference.

TECHNICAL FIELD

The present invention relates to a missile warning system and moreparticularly, relates to an active electro-optic missile warning andtracking system.

BACKGROUND INFORMATION

Existing solutions rely on detecting and tracking the thermal signatureof the missile, either from the propellant exhaust or the heating of themissile body.

When such methods rely on ultraviolet radiation, they can only detectand track the missile while the motor is in operation. This is alimiting capability with missiles that “burn-out” long before impact.

When such methods rely on infrared radiation, they can track bothmissile exhaust and body heating. However, there is an enormous amountof infrared clutter in most background scenes. This clutter placessignificant limitations on the ability to detect and track missilesusing passive infrared radiation.

A need exists for a missile detection system and method that canaccurately detect missiles even in a cluttered environment. The systemand method should preferably be able to detect the location of missile.Moreover, the system and method should preferably be able to detect amissile prior to launch, not simply while in-flight.

Optical Augmentation is a recognized approach to detecting opticalsystems in a scene. The conventional method relies on the dramaticallyincreased apparent cross section of an optical system when the source ofillumination and detection are in the field of view of the opticalsystem being sought.

This is the phenomenon responsible for the glow of cat's eyes at nightand the red-eye apparent in photographic subjects when a direct flash isused.

A second less familiar phenomenon is the brevity of the impulse responseof such an optical system. Because the incoming light is reflected off asingle point in the focal plane, an incoming impulse of light isretro-reflected with small fractions of a nanosecond of response time.Virtually all other objects in the scene will have a much longer impulseresponse making the optics “stand-out” in time.

The combination of these two phenomena can be used to implement a veryeffective approach to electro-optic missile warning.

SUMMARY

A threat detection system, according to one embodiment of the presentinvention, is capable of detecting a potential weapon during flight orprior to launch. The threat detection system includes a laser energysource that generates a laser energy pulse. The oscillator modulates thelaser source to generate a laser energy signal having a predeterminedfrequency and pulse time. Each pulse is short enough (a few tenths of ananosecond) such that the laser energy signal reflected off an opticalsystem can be readily distinguished from one reflected off other objectsin the scene. The receiving system creates an image of the receivedreflections from the scene. Threat systems that use optical systems willexhibit three concurrent features. First, the pulses from those systemswill be very short in time (a few tenths of a nanosecond). Second, thesepulses will be very large in magnitude compared to the light returningfrom adjacent areas in the scene. Third, the light from threat systemswill occupy a very small portion of the scene (typically less than onepixel). The receiving system looks for some combination of these threefeatures (short time, high relative magnitude, small size) todistinguish electro-optic threats from other objects.

Optionally, the threat detection system includes a plurality ofoscillators such that a plurality of different frequencies and/or pulsetimes can be generated to distinguish between returns that occur betweentwo pulses and those that take longer than one repetition interval toreturn.

An emitter (preferably a wide-angle lens) is coupled to the oscillatorand transmits the laser signal non-directionally. Optionally, the threatdetection system includes a plurality of emitters disposed proximate anouter surface of the object to be protected in order to provide anadequate emission coverage pattern. A receiver is arranged to receivelaser energy signal transmitted by the emitter that has reflected off anoptic of a potential weapon. A comparator then analyzes the reflectedlaser signal in synchrony with the transmitted laser signal to determinea direction, a distance, and a speed of the potential weapon ortargeting system.

It is important to note that the present invention is not intended to belimited to a system or method which must satisfy one or more of anystated or implied objects or features of the invention. Modificationsand substitutions by one of ordinary skill in the art are considered tobe within the scope of the present invention, which is not to be limitedexcept by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reading the following detailed description, takentogether with the drawings wherein:

FIG. 1 is plan view of one embodiment of the threat detection system incombination with several types of objects to be protected;

FIG. 2 is a schematic view of another embodiment of the threat detectionsystem according to the present invention; and

FIG. 3 is a flow chart illustrating one embodiment of the threatdetection method according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A threat warning or detection system 10, FIG. 1, and method 300, FIG. 3,according to one embodiment of the present invention, detects thepresence of a potential weapons 16, FIG. 1, (such as, but not limitedto, a missile, an aircraft, a vehicle, a vessel, or the like) within acoverage area 13 around an object 11 of interest (such as, but notlimited to, manned and unmanned aircrafts, vehicles, vessels, andbuildings). The threat detection system 10 transmits a non-directionallaser signal 12 that is capable of detecting a potential weapon 16 thatis pointed or aimed at the object 11 to be protected while in flight orprior to launch.

The threat detection system 10, according to one embodiment of thepresent invention, takes advantage of the fact that modern potentialweapons 16 include highly sophisticated optic systems 14 used to guidethe potential weapon 16 and recognizes that extremely short (fraction ofa nanosecond) laser pulses 12 reflect very well off the optics 14 ofpotential weapon 16 that are pointed or aimed at the source 11 of thelaser pulse 12 as will be explained in greater detailed hereinbelow.Consequently, the threat detection system 10 is not limited to detectingpotential weapons 16 only in-flight, but rather is also capable ofdetecting optics 14 of potential weapons 16 that are aimed at an objectto be protected 11 prior to the potential weapon 16 being launched.

The threat detection system 10, FIG. 2, includes at least one laserenergy source or generator 20, at least one oscillator 22, and at leastone controller 24. The laser source 20 generates a high-powered laser,act 310, and is coupled to at least one oscillator 22. The oscillator 22modulates the laser energy generated by the laser source 20 to thedesired frequency and pulse time, act 320. The oscillator frequency mayrange from as low as a few Hz to as high as several hundred kilo-Hz. Thepulses may range from a significant fraction of a joule at low pulserates to a milli-joule at high rates. The tradeoff being driven by theavailability of LASER sources and the anticipated distance to andcross-sections of the targets.

The length or time of the pulse must be short enough such that thethreat detection system 10 can differentiate and distinguish betweenoptics 14 and other objects or background clutter. The exact pulse timeof the laser signal 12 will depend upon the specific types of missiles14 that the threat detection system 10 is intended to detect, and iswithin the ordinary knowledge of one skilled in the art and can bedetermined without undue experimentation. While not a limitation of thepresent invention, a pulse time of a few tenths of a nanosecond isbelieved to be sufficiently short to enable the threat detection system10 to differentiate and distinguish between the optics 14 of mostpotential weapons 16 and other objects or background clutter.

The controller 24 is coupled to both the laser energy source 20 andoscillator 22. The controller 24 activates the laser source 20,determines the intensity of the resulting laser signal 12, as well asactivates a countermeasure system (not shown) or otherwise providesnotification of a potential threat 16. The controller 24 also regulatesthe oscillator 22 to generate the laser signal 12 having a specificfrequency or frequency range. Additionally, the controller 24 includesmemory 25 and an internal clock 27 that stores information pertaining tothe pulsed laser signal 12 such as, but not limited to, the time of thepulse, the frequency, length of the pulse, and intensity. As will bediscussed hereinbelow, this information is compared with receivedsignals 18.

The output of the oscillator 22 is coupled to a transmitter 26 such asan emitter or lens (for example, a fisheye or wide-angle lens). Theemitter 26 transmits the pulsed laser signal 12 non-directionally. Asused herein, the term non-directionally is intended to denote that thepulsed laser signal 12 is not aimed directly at a specific object. Theexact coverage pattern and number of emitters 26 will depend upon thecircumstances of the installation.

For illustrative purposes only, an aircraft 11′ (FIG. 1) may includetwo, 180 degree hemispherical emitters 26, a first emitter 26′ disposedabout an upper surface of the aircraft 11′ and a second emitter 26″disposed about a lower surface of the aircraft 11′. This arrangement ofemitters 26 is believed to provide the aircraft 11′ with anapproximately 360 degree, spherical coverage pattern. In contrast, asingle, generally spherical emitter 26 may be sufficient when used toprotect a building 11″ where it is unlikely that 360-degree, sphericalcoverage would be needed. It is important to note that otherarrangements of emitters 26, oscillators 22, and laser generators 20 areenvisioned and are within the scope of the present invention.

The transmitted, pulsed laser signal 12 travels until it reaches theoptics 14 of a potential weapon 16 that is pointed at the object 11 tobe protected or until it dissipates. The threat detection system 10takes advantage of the fact that the optics 14 of potential weapons 16are designed to precisely focus light coming from the object to beprotected onto the threat imaging system focal plane. Because the pulsedlaser signal 12 is extremely short, only optics 14 that are pointed atthe object 11 to be protected will reflect the pulsed signal 12 backtowards the object 11 to be protected. All that is necessary is for theobject to be protected to be in the field-of-view of the threat sensor,which is always true for any threat. Other objects, such as backgroundclutter and the like, will reflect the light across a distributedsurface so the result is spread out in time unlike the short-timeretro-reflection from an imaging system.

The reflected signal 18 is then received by the receiver 28, act 340, ofthe threat detection system 10. It should be noted that the threatdetection system 10 may include one or more receivers 28.

The received signal 18 is then compared with the transmitted signal 12,act 350, by the comparer 30. Using focal plane detection techniques, thecomparer 30 analyzes the spatial distribution and optical data orcharacteristics (such as, but not limited to, the time of the receivedsignal 18, the frequency, length of the pulse, and intensity) of thereceived signal 18 with the characteristics of the transmitted signal 12stored in the memory 25 of the controller 24. Based on this comparison,the comparer 30 determines if the received signal 18 is that of apotential weapon 16 or background clutter, act 360, and determines thedirection of the potential weapon 16 (act 370), the distance of thepotential weapon 16 (act 380), and the rate of closure of the potentialweapon 16 (act 390). With sufficiently rapid sampling of the impulseresponse of the threat optical system, it is also possible to match theoptical time response to a database of signatures and thereby identifythe type of threat.

Accordingly, the threat detection system 10 of the present invention isable to detect a potential weapon 16 not only while in flight, but alsowhen the optics 14 of the potential weapon 16 are aimed at the object 11to be protected prior to the launch of the potential weapon 16. As aresult, countermeasure systems and methods/actions designed to protectthe object 11 (for example, missile jamming systems and evasivemaneuvers) can be activated sooner, thus increasing the likelihood thatthe potential weapon 16 will not hit the intended target.

Additionally, the threat detection system 10 transmits a non-directionalpulse laser signal 12 and therefore provides a greater and more completecoverage pattern 13 than traditional systems that must scan or beotherwise aimed at a particular area. Because the threat detectionsystem 10 does not include any externally moving parts (such as arotating housing or the like), the overall maintenance of the threatdetection system 10 is greatly reduced. Lastly, the overall size of thethreat detection system 10 is significantly reduced, thereby allowingthe threat detection system 10 to be installed more easily on a widevariety of object 11 to be protected.

As mentioned above, the present invention is not intended to be limitedto a system or method which must satisfy one or more of and stated orimplied objects or features of the invention and should not be limitedto the preferred, exemplary, or primary embodiment(s) described herein.Modifications and substitutions by one of ordinary skill in the art areconsidered to be within the scope of the present invention, which is notto be limited except by the following claims.

1. A threat detection system for the detection of a potential weaponhaving an optic element with respect to an object to be protected, saidthreat detection system comprising: a laser energy source, said lasersource for generating a laser beam in response to a laser energy sourcecontrol signal; at least one oscillator, coupled to said laser energysource, said at least one oscillator responsive to an oscillator controlsignal and configured for modulating said laser beam to generate a lasersignal to be transmitted toward at least a scene to be inspected for apotential weapon, said laser signal having a predetermined frequency andpulse time controlled by said at least one oscillator, wherein saidpulse time is selected to be short enough to cause a reflection of saidlaser signal from an optic element of an optical guidance system of saidpotential weapon that is much greater than a reflection of said lasersignal from other elements of the scene including said potential weapon;a controller, coupled to said laser energy source and to said at leastone oscillator, and configured for providing said laser energy sourcecontrol signal and said at least one oscillator control signal, saidlaser energy source control signal for activating the laser source, saidat least one oscillator control signal for regulating the frequency ofsaid at least one oscillator; an emitter, coupled to said oscillator,and configured for transmitting said generated laser signalnon-directionally; a receiver, configured for receiving at least aportion of a laser signal transmitted by said emitter that has reflectedoff the optic element of said potential weapon; and a comparer, coupledto said receiver, and configured for analyzing and comparing saidreflected laser signal with said transmitted laser signal to determine adirection, a distance, and a speed of said potential weapon with respectto said object to be protected, said comparer configured for identifyingselected characteristics of said reflected laser signal, wherein saidselected characteristics include two or more characteristics selectedfrom the group of characteristics consisting of: reflected laser signalenergy pulses having the shortest time duration; reflected laser signalenergy pulses having a large magnitude compared to reflected lasersignal energy pulses from adjacent areas in the scene; and reflectedlaser signal energy pulses occupying a very small portion of the scene.2. The threat detection system as claimed in claim 1 wherein saidemitter includes a wide-angle lens.
 3. The threat detection system asclaimed in claim 1 wherein said at least one oscillator includes aplurality of oscillators, wherein each of said plurality of oscillatorsis configured for generating a laser signal having a different frequencyand pulse time from another of said plurality of oscillators.
 4. Thethreat detection system as claimed in claim 1 wherein said emitterincludes a plurality of emitters disposed proximate an exterior surfaceof said object to be protected.
 5. The threat detection system asclaimed in claim 1 wherein said at least one controller determines saidfrequency and said pulse time of said transmitted laser signal andstores data concerning said transmitted laser signal.
 6. The threatdetection system as claimed in claim 5 wherein said at least onecontroller is coupled to said comparer, and wherein said compareranalyzes said data concerning said transmitted laser signal stored insaid controller with said reflected laser signal to determine saiddirection, said distance, and said speed of said potential weapon. 7.The threat detection system as claimed in claim 6 wherein said compareruses focal plane detection techniques to determine said direction, saiddistance, and said speed of said potential weapon.
 8. The threatdetection system as claimed in claim 1 wherein said pulse time is a fewtenths of a nanosecond.
 9. A method of detecting a potential weaponhaving an optic element with respect to an object to be protected, saidmethod comprising the acts of: generating a laser beam in response to alaser energy source control signal; modulating said laser beam togenerate a laser signal having a predetermined frequency and pulse time,wherein said pulse time is selected to be short enough to cause areflection of said laser signal from an optic element of an opticalguidance system of a potential weapon that is much greater than areflection of said laser signal from other elements of a sceneirradiated with said laser signal; transmitting said laser signalnon-directionally to at least said scene; receiving a reflected lasersignal, wherein said reflected laser signal may include a portion of alaser signal transmitted by said emitter that has reflected off saidoptic element of said potential weapon; comparing a direction, speed anddistance of said reflected laser signal with a direction speed anddistance of said transmitted signal; determining a type of saidpotential weapon based on said comparison; and determining whether saidpotential weapon is a threat.
 10. The method as claimed in claim 9further including the act of storing data concerning said transmittedlaser signal.
 11. The method as claimed in claim 10 wherein said act ofdetermining if said reflected signal is a potential weapon includescomparing said reflected laser signal with said data concerning saidtransmitted laser signal.
 12. The method as claimed in claim 9 whereinsaid act of comparing said reflected laser signal with said data of saidtransmitted laser signal includes using focal plane detectiontechniques.
 13. The method as claimed in claim 9 wherein said pulse timeis a few tenths of a nanosecond.
 14. A threat detection system fordetecting a weapon comprising: means for generating a laser beam; meansfor modulating said laser beam to create a laser signal to betransmitted toward at least a scene to be inspected for a potentialweapon, said laser signal having a predetermined frequency and pulsetime, wherein said pulse time is selected to be short enough to cause areflection of said laser signal from an optical component of an optictransceiver of a potential weapon that is much greater than a reflectionfrom other elements of the scene; means for transmitting said lasersignal non-directionally towards at least said scene; means forreceiving a reflected laser signal, said reflected laser signalincluding at least said transmitted laser signal that has reflected offthe optical component of a potential weapon; and means for comparing adirection, a speed and a distance of said reflected laser signal with adirection, a speed and a distance of said transmitted laser signal todetermine if said potential weapon is a threat, wherein the comparercompares said reflected laser signal with said transmitted laser signalto determined a type of said potential weapon.